Electronic displays facilitate the reproduction of data on a lighted platform. Driving circuitry is employed to manipulate lighted elements to render the information being displayed. The viewer may gaze upon the display and view the lighted elements to process and consume the information.
However, because light is employed to convey the electronic information, the viewing experience is affected by the environment in which the electronic display is implemented in. For example, if the electronic display is an awkward or inconvenient location, viewing the electronic display may be ultimately frustrated.
Further, the environment around the electronic display may be dynamic and changing. For example, if the electronic display is implemented in an area that interacts with outside or external light providing sources, the electronic display's ability to convey information via the lighted elements may be obstructed or modified.
A measure of unit for determining the intensity of light being transmitted or propagated in a specific direction is known as luminance. Various units may be employed to measure luminance, such as a candela per square meter. One of ordinary skill in the art may appreciate that several units or types of measurements may be employed for luminance measurement.
For example, if an electronic display is implemented in a vehicle, the electronic display may interact with the outside lighting environment. Thus, several factors may be present with the exterior lighting to affect the display's ability to provide a clear display in an optimal fashion. For example, the exterior lighting may be affected by the cloud cover, the weather, the road (e.g. if the vehicle is in a tunnel), the time of day, or the like.
Thus, an electronic display may be aided greatly by an ability to be cognizant of the exterior lighting conditions. Based on the knowledge of the exterior lighting conditions, the electronic display may adjust the display luminance accordingly.
One such example of a system for adjusting display luminance is shown in FIG. 1. FIG. 1 illustrates an example of a system 100 for adjusting display luminance according to a conventional implementation. Because the system 100 is known in the prior art, a detailed explanation will be omitted. System 100 is referred to as a linear light system. Linear light systems may not work over specific dynamic ranges, such as 6-8 decades. Over these dynamic ranges, an analog-to-digital converter may be inadequate.
FIG. 2 illustrates an example of a process for determining ambient display background luminance (DBL). Referring to FIG. 2, with the aspects shown, if various factors are known, such as a reflection coefficient or luminance level, the DBL may be calculated.
As shown in FIG. 2, various component reflection coefficients (R1 . . . Rn) are associated with luminance factors. These luminance factors may be employed to determine the DBL.
The aspects shown in FIG. 2, may be employed with conventional systems for ambient luminance detection. For example, in the vehicular context, the following factors may be sensed, the lambertian diffuse, specular, and haze diffuse.
FIG. 3(a) illustrates an example of how reflection of light onto an electronic display 300 may be measured via a light receiving source (i.e. one eyes) 310. Referring to FIG. 3(a), a point source 320 generates light 325 onto a display 300. The display 300 reflects the light 325 onto a light receiving source 310, via an angle 315. Employing mathematical relationships known to one of ordinary skill in the art, a reflection factor β, the angle 315, a system may determine the ambient light caused by reflection off a display.
FIG. 3(b) indicates a luminance graph 350 with source inclinations relative to a specular direction (angle 315). The y-axis, and the ranges provided indicate an associated effect that may cause various luminance modifications at different angles.
The various affects shown in FIG. 3(b) may cause the viewer of the electronic display 300 to see various background luminance (DBL). Thus, as the DBL increases, the luminance of the display may increase at a corresponding amount to counteract the DBL effects.
In order to understand how to adjust display luminance, the Silverstein relationship is provided (as explained in several references submitted). The equation described below describes a relationship between the detect DBL and the luminance to be employed in a display.ESL=BO(DBL)C                the terms being defined as:        ESL=Emitted Symbol Luminance in cd/m2        BO=Luminance Offset Constant        DBL=Various Display Background Luminance in cd/m2         c=Power Constant (slope of the power function in logarithmic coordinates).        
With cathode ray tubes (CRT) display technologies, phosphor reflectance does not change as a function of phosphor light emission. A liquid crystal display (LCD) presents a different challenge due to the “on” and “off” state each LCD cell experiences. Thus, variations of the Silverstein relationship may be calculated for LCD displays. However, by employing the DBL relationship above, the display visibility may be greatly improved.
In addition, various other factors employing the Silverstein methodology may be employed. For example, the gain correction factor (GF) may be calculated, which employs a forward looking light sensor.
However, the existing logarithmic sensors to compensate for light adaptation effects may be incompatible with the Silverstein methodology (which is designed an optimized for linear light sensing). Thus, employing a logarithmic light sensor in a display adjustment system may ultimately be frustrated.